fixed compiler warnings reported by gcc/clang

* changed some catch blocks to use exception references instead of value types
 * fixed missing use of SCR_WIDTH/SCR_HEIGHT for glfwCreateWindow
 * fixed implicit numeric type casts regarding signedness
 * removed unused variables

Signed-off-by: Toni Uhlig <matzeton@googlemail.com>

src/5.advanced_lighting/9.ssao/ssao.cpp

@@ -302,7 +302,6 @@ int main()
         shaderLightingPass.setVec3("light.Position", lightPosView);
         shaderLightingPass.setVec3("light.Color", lightColor);
         // Update attenuation parameters
-        const float constant  = 1.0; // note that we don't send this to the shader, we assume it is always 1.0 (in our case)
         const float linear    = 0.09;
         const float quadratic = 0.032;
         shaderLightingPass.setFloat("light.Linear", linear);